Field
This disclosure relates to a binder composition for a secondary battery, a cathode and a lithium battery including the binder composition.
Description of the Related Technology
Lithium batteries are used for various purposes due to their high voltage and high energy density. For example, an area of electrical vehicles (e.g., HEV and PHEV) requires a lithium battery capable of operating at a high temperature, charging and discharging a large amount of electricity, enabling long-term use and having high energy density and excellent cycle life characteristics.
Relative amounts of electrode active material and conducting agent need to be increased and binder needs to be decreased in an electrode to provide a lithium battery with high energy density and excellent life characteristics. However, when the amount of a binder decreases, dispersibility and adhesiveness of the electrode active material and/or the conducting agent and flexibility of an electrode active material layer may decrease. Thus, cycle life characteristics of lithium battery may be deteriorated due to detachment of the electrode active material from a current collector during charging and discharging the lithium battery. Therefore, a binder capable of providing enhanced dispersibility of an electrode active material and/or a conducting agent, enhanced adhesiveness of an electrode active material and/or a conducting agent with respect to a current collector, and enhanced flexibility of the electrode plate with a small amount of the binder is needed.
For example, a fluorine containing binder, such as a poly(vinylidene fluoride) (PVDF) not containing a polar group, is hardly swelled in an organic electrolyte solution and thus is useful in maintaining an electrode structure while operating a battery and may improve dispersibility of an electrode active material. However, the fluorine containing binder, such as PVDF not containing a polar group, provides poor dispersibility of a conducting agent, poor adhesiveness to the electrode plate, and poor flexibility of the electrode plate.
Moreover, a non-fluorine containing binder, such as an acrylonitrile-butadiene hydride, provides enhanced dispersibility of a conducting agent and enhanced flexibility of the electrode plate than those of the fluorine containing binder, but adhesiveness to a current collector is still poor.
Therefore, a binder capable of overcoming the problems of the conventional art and improving energy density and cycle life characteristics of a lithium battery by providing improved adhesiveness and flexibility at the same time is needed.